The work aims at better understanding the basic mechanisms and kinetics of leaching of irradiated uranium oxide and mixed oxide fuel. In addition to real fuel samples, well-defined synthetic fuel forms will be used and solid state physical techniques will be employed, for example, for single effect studies (such as radiolysis, inter-surface state, groundwater composition and redox conditions) in order to assist the interpretation of the results obtained with spent fuel. For the determination of the source term of spent fuel, instruments and methods will be further improved. Experimental results will be compared with theoretical predictions. For in-situ measurements, electrochemical corrosion studies and thin film simulation experiments will be used. Rationale The management of spent nuclear fuel and highly radioactive waste is of considerable importance as about 45000 t of irradiated fuel is in interim storage in the EU. Decisions are needed on the options to be explored and to be pursued (example, law 1991 of French Parliament).

The two approaches for spent nuclear fuel management favoured by the Member States of the European Union can be schematised as follows: intermediate storage with subsequent conditioning for final disposal, and intermediate storage with subsequent reprocessing (partitioning) for lowering the radiotoxicity (transmutation) before final disposal in geological formations. Detailed design proposals for final repositories for spent fuel are now under regulatory review in some Member States as a part of a stepwise procedure. In the mean time, there are adequate facilities for safe short-term storage of spent fuel and high level waste. Development of a common understanding of the frequently used concept of "reasonable assurance of safety" for the long-term, post-closure phase of final repositories is highly desirable to ensure reasonably equivalent legal interpretations among EU countries in the environmental impact assessment and licensing procedures.